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Old 11-19-2008, 06:11 PM   #1
dion
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Mastic or thinset? :confused:

Hello,

What is the difference between mastic and thinset? My husband and I are tiling our tub surround and have bought a bucket of Omnigrip. However, after poking around various threads, it seems that Omnigrip is a mastic, not a thinset and I shouldn't use it. Is this correct?

Custom Building Products offers a pre-mixed thinset called Simpleset. It contains acrylic copolymer. Versabond is also an option and a couple other threads mention using it around the tub surround. Which of these should I go with? Or is there something even better that I haven't listed?

I'd be greatly appreciative of any advice (well, not any advice...)
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Old 11-19-2008, 06:14 PM   #2
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Hi Dion. Yeah, that's mastic, take it back and get the Versabond. You don't want anything premixed.
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Old 11-19-2008, 06:18 PM   #3
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Hi Davy,

Thanks for the speedy reply. What's the difference between mastic and thinset?
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Old 11-19-2008, 06:27 PM   #4
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Dion,

In simple terms; Mastic is bad and is expensive, while thin set is good and cheap! Sounds backwards huh?

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Old 11-19-2008, 06:34 PM   #5
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Quote:
What's the difference between mastic and thinset?
Mastic is a high polymer petroleum distillate and can stay soft in a bucket for a long time.

a thinset is a blend of portland cement, calcium carbonate, co polymers and silica sand, when water is added to it has a chemical reaction and turns hard like concrete but with a super grip.

this reaction can happen with air or water or without air.
mastic needs air to dry, so if it stays soft in a bucket with no air, how wil it dry under the tile with no air ......very slowly.
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Old 11-19-2008, 06:44 PM   #6
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Yep, what the others said. Mastic can also emulsify when moisture gets to it. It doesn't breathe like a cement product (thinset) and mold loves the stuff. It's fine for dry areas but not in a shower or over a bathtub.
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Old 11-19-2008, 06:47 PM   #7
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Mastic is essentially a (typically) water soluable glue. It needs to dry out to firm up. It can sit in an air-tight bucket for extended time and be soft because no water or air can get to it. Put it on a wall, cover it with nearly waterproof tile, then let a little moisture get back in through the grout (and it will) and more if any water pools. It can take a very long time to dry out and attain max strength under a big tile. Smaller tiles have more joints, and more opportunity for it to dry.

Thinset is partially made of cement. Once it cures (it doesn't need to dry - more later, though), it retains its strength and isn't affected by getting wet again. Mastic can get soft again like it was in the bucket if it gets wet.

A modified thinset has a bunch of proprietary addatives. They make the thinset stickier, a little stronger bond, and a little flexible. Those parts need to dry, but once dry typically aren't affected (once the cement fully cures) by getting wet again (some modified thisets shouldn't be used in places like holding tile in a pool like underwater or a continuous spray like in a fountain).

So, for mastic...don't use when it will get sprayed or wetted regularly or with large tile so it has a chance to dry (walls outside of the shower are okay - thinset is cheaper). Thinset of one sort or the other can be used nearly anywhere you tile.
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Old 11-19-2008, 07:09 PM   #8
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Hello All,

I can now make the educated decision to return the Omnigrip and buy some modified thinset. Even though my tiles are small (4 X 4) and will allow more air to get to the mastic, more air also = potential for more water too. It's not worth the risk.

Thank you for your replies.
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Old 11-19-2008, 07:35 PM   #9
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Quote:
= potential for more water too. It's not worth the risk.
no it isn't.

you also need some type of waterproofing or a vapor barrier in your shower.
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Old 11-20-2008, 12:41 PM   #10
Paulie Walnuts
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With Durrock being produced at the rate it has. Alot of times it's not fully dry when you buy. This can be a nightmare if you use any type of Mastic. Thinset is always a good call in bathrooms.
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Old 11-20-2008, 05:56 PM   #11
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Hello Brian,

Are you agreeing with me, or telling me that I got it all wrong?

Quote:
= potential for more water too. It's not worth the risk.
no it isn't.

you also need some type of waterproofing or a vapor barrier in your shower.
I did return the Omnigrip and purchased Versabond.

Thanks for including that picture. What a nightmare. With the help of this forum, I'm REALLY hoping that doesn't happen to us. We've been trying to follow the advice of various threads so up to this point, we've ripped down all the old sheetrock, installed roofing felt paper, tarred the seams, and are now putting hardibacker over top. Can you tell me though, should we tape the seams just before we're going to set the tile, or should we tape the seams ahead of time, let the thinset dry, and then tile? If we tape ahead of time, then we're going to have areas of hardened thinset that we'll have to apply another layer of thinset over top of when tiling. (I hope I'm making sense).

Kirstin
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Old 11-20-2008, 06:05 PM   #12
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clarification: "no it isn't.......worth the risk.....to use Mastic."

Quote:
should we tape the seams just before we're going to set the tile,
I tape and then set tile over at the same time.
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Old 11-20-2008, 06:32 PM   #13
Brian in San Diego
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Quote:
Originally Posted by Dion
We've been trying to follow the advice of various threads so up to this point, we've ripped down all the old sheetrock, installed roofing felt paper, tarred the seams, and are now putting hardibacker over top.
Just for clarification where did you terminate the tar paper? Is it terminated inside the lip of the tub?

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Old 11-22-2008, 09:37 AM   #14
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Hello Brian in San Diego,

We terminated the tar paper inside of the tub flange in order to get water to come back into the tub. The paper's edge is pressed into the roofing tar.

Thanks for your help,
Kirstin
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Old 11-22-2008, 10:33 AM   #15
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